<!DOCTYPE html>
<html>
<body>
<p>Click the button to get the value of outer HTML before remove demo.</p>

<button onclick="myFunction()">Try it</button>

<p>Click the button to get the value of outer HTML after remove demo.</p>

<button onclick="myFunction2()">Remove demo</button>

<p id="demo"></p>

<script>
function myFunction() {
  var a = document.getElementsByTagName("HTML")[0];
  window.alert(a.outerHTML);
}

function myFunction2() {
  document.getElementById('demo').remove();
  var a = document.getElementsByTagName("HTML")[0];
  window.alert(a.outerHTML);
}

</script>

</body>
</html>
